The measurement of skin reflectance finds a particular application in pathology and in cosmetology. In particular, skin reflectance may be associated to other parameters such as the rate of secretion of sebum. The measurement of reflectance then becomes useful in the study of seborrhea. It may also present an advantage for studying other skin diseases such as lichen, SSM. . . . In cosmetology, the invention finds an application in measuring the effect of products known as "anti-reflectance" products for greasy skins, particularly for making efficiency-aimed tests. Another application of the present invention could be the grading of different types of skins.
Various methods and devices already exist for measuring surface reflectance, for example in the industry of paints and varnishes, in order to determine the characteristics of reflection of coated surfaces. It has also been proposed to use reflectance measurement to determine a surface finish.
All said known methods and processes which are used in industry are not applicable to the measurement of skin reflectance.
A first problem to be solved with this particular application is the problem of influence of color. Indeed, with the known devices which can only measure the specular reflection, the results obtained for different surfaces are only comparable if the surfaces are all of the same color.
To overcome the effect of color, it has been proposed to substitute to the specular reflection absolute measurement, a relative measurement between specular reflection and diffuse reflection. However, the known devices using such relative measurement remain inappropriate for measuring skin reflectance.
Indeed, the apparatuses used in industry, generally comprise optical systems with focusing lenses which require an accurate positioning of the measuring apparatus with respect to the surface of which the reflectance is being measured. It is then necessary for said surface to be flat and for the measuring area to be, in general, of relatively large dimensions.
Yet, in the case of the skin, the measuring area has to be relatively small in order to keep the characteristics of the skin uniform in that area and to make the measurement on as flat a surface as possible, without changing the characteristics to be measured by a flattening of the skin.
It is also important to have a measuring apparatus which is easy to handle and requires no higher accurate positioning with respect to the skin.